This invention relates to bar codes used in the processing of mail pieces.
In many countries a postal code is used to facilitate automation in sorting. In Canada, the postal code contains three alphabetic characters (letters) interleaved with three numeric characters (numbers) while in the U.S.A. the zip code consists of five numbers. If a customer has applied the postal code to an envelope this is converted by an optical character reader (O.C.R.) and computer in the Post Office to a bar code which is then printed on the envelope. If the customer has not applied the postal code, this will be generated in the Post Office and the bar code will be printed on the envelope as before.
It is also becoming more usual for the large corporate customer to apply the postal code in bar code format. A bar code is used because it is easier to read automatically than alphanumeric characters.
The British Post Office (BPO) has developed a 4 state bar code. The four possible states are one which comprises only a tracker element, one which comprises a tracker element and an ascender element, one which comprises a tracker element and a descender element and one which comprises a tracker element, an ascender element and a descender element. These elements will be described in detail hereinbelow.
The BPO code uses four bars to represent each alphanumeric character but for error protection each character must have two ascenders and two descenders which limits the number of possible combinations to 36. Error detection is dealt with by including a check sum. The BPO code is intended to be printed by customers (mailers) to encode sortation information.
The BPO code uses a single bar to indicate the start of the code and a different single bar to indicate the end of the code. The start/stop bars in the BPO code can easily be confused and can result in decoding of an upside down bar code.
A paper entitled "A Damage Resistant Bar Code for the Royal Mail" by Blahut et al, 1992 discusses an improvement of the BPO bar code which essentially makes the BPO code more robust by adding Reed-Solomon error correction to handle missing bars (erasures) and bar print errors. The encoding is based on codewords of two bars each--a left and right codeword--and the interleaving of the codewords to form a bar code. Blahut has also identified some decoding logic to recover from missing or incorrect bars and overcome the weakness of the start/stop pattern with decoding logic. The Blahut Code is intended to be printed by the Post Office as an internal code and only postal sortation data is encoded.
It is an object of the present invention to improve on the BPO and Blahut codes by offering a robust code which is sufficiently flexible that it may be applied by the Post Office or the customer and which can be used not only for the postal code but for route sequencing, track and tracing, revenue accounting and other customer information as well as customer service information such as return mail management, automated data entry of customer information and the like.